Ecological responses of coastal benthic macrofauna to phosphogypsum industrial waste in the Gulf of Gabès (central Mediterranean Sea).

Abstract

The Gulf of Gabès is subject to intense anthropogenic pressure, mainly from coastal urbanization and phosphate industry activities, including phosphogypsum and effluent discharges. The present study investigated the response of macrobenthic communities to uncontrolled phosphogypsum effluents in the coastal zone of Gabès, based on a two-year seasonal monitoring survey. Twenty sampling stations located downstream from major potential pollution sources were monitored seasonally. A total of 182 macrobenthic taxa were identified, belonging to eight animal phyla and 104 families. Crustaceans (38.5%), molluscs (31%) and polychaetes (18.5%) were the most dominant groups. Statistical analyses, including ANOVA and cluster analysis, revealed a clear spatial gradient in community structure, influenced by both environmental variables and anthropogenic stressors. Inner stations, closer to industrial effluents, showed the lowest taxonomic richness and abundance, associated with high levels of heavy metals and organic enrichment, while offshore stations exhibited the highest values. Univariate diversity metrics demonstrated a general trend of increasing species diversity with distance from the pollution source. Polluted stations were predominantly colonized by carnivorous and selective deposit-feeding taxa, whose distribution appeared more strongly driven by trophic resource availability than by direct pollution stress. Seasonal variations in faunal abundance, diversity, and community composition were largely attributed to the biological cycles of the dominant species. The multiple biotic indices (AMBI, M-AMBI, BO2A, and BENTIX) classified the coastal ecological status from poor to good, following the spatial pollution gradient. This study underscores the importance of two-year investigation for improving understanding of benthic community dynamics and to support effective management and conservation strategies in this disturbed central Mediterranean ecosystem.